________Time_______________________Plant Mass________ _ ________Amount of Water ____________Amount of Soil

Cup with Soil and No Plant

PART ONE
Does plant mass

Materials

• Small cups to retain water
• Soil
• Seeds of mung beans, lima beans, or peas
• Balance or scale
• Graduated cylinder

- WATER
come from water?

Procedures

• Begin with sprouted lima beans and moistened soil in 4 small cups
• Mass cup, soil and sprouted seeds
• Measure and add just enough water to moisten the soil
• Add the same amount of water daily (10 ml = 10 grams)
• Add the same amount of soil to 5th cup
• Weigh and record the mass of each cup daily.
• Record the amount (volume/mass) of water added.

PART TWO - THE SOIL
Does plant mass come from the soil?

DAY 1_____________________________________DAY 14

DATA COLLECTION DAY 1

DATA COLLECTION DAY 14

ANALYSIS PART TWO

• From the graph of the above data one can see that the increase in plant mass was more than the mass lost by the soil.
• The average increase in plant mass over 14 days was 3.2 grams.
• The average mass lost by the soil was 1.3 grams.
• The average difference in plant mass increase and soil mass loss was 1.9 grams.

Therefore, where did the increase in plant mass come from?

Let's look at the equation for photosynthesis:

What are we missing?

CONCLUSION PART TWO

• In the 17th century a Flemish physician, chemist, and physicist named Jan Baptista van Helmont performed a 5 year study in which he massed the soil of a willow tree in a pot and after 5 years found that the willow had gained a tremendous amount of mass and soil had lost very little. Van Helmont believed that water was the source of the plant mass.
  
• As we tried to investigate water earlier, we were unable to prove that hypothesis. John Woodward, a professor and physician at Cambridge University in the late 17th century, tried to design an experiment to test the hypothesis that water was the source of the extra mass. In a series of experiments over 77 days, Woodward had seen the same results as this study and he also rejected the hypothesis that plant growth comes from water.
  
• It wasn't until 1771 that an English chemist, Joseph Priestly, began to experiment with plants and the air. He made a major breakthrough which led us to the understanding that the plant mass actually does come from the air in the form of carbon dioxide. This fact was not confirmed until 1940 when Martin Kamen discovered carbon-14 which could be used to trace the carbon in carbon dioxide through photosynthesis.